Combustion systems that operate with a mixture of oxygen and recirculated flue gas as the oxidant that combusts with the fuel, are currently in development to facilitate the generation of carbon dioxide in concentrations that make recovery and isolation of the carbon dioxide more feasible. Such systems, often referred to as oxy-fuel combustion systems, typically include a burner to combust the fuel gas with oxygen that also contains recirculated flue gas. A flue gas recirculation loop and control systems are included, for providing fuel gas and oxygen and gaseous products of the combustion back to the burner to adjust the furnace heat transfer to levels similar to air combustion.
Ultra-low NOx gas burners, often referred to as “premixed” burners, are optimized to provide very low NOx emissions from their use in industrial gas boilers. These burners use multiple gas nozzles through which the fuel gas is fed, to facilitate premixing of the fuel gas into the combustion air (i.e., the air that is the source of the oxygen that combusts with the fuel gas) to distribute the fuel more evenly into the combustion air. This more diluted fuel gas results in a more even heat release upon combustion, leading to lower thermal NOx emission from the flame. However, the ignition stability and flame stability of such burners is a challenge, so the burners provide adjustability for fuel and combustion air to achieve the best possible flame stability and NOx emissions.
The present inventors have determined that when a premixed ultra-low NOx gas burner is operated with a mixture of oxygen and recirculated flue gas as the gaseous oxidant, the system may experience flame instability and potential flame failure. This would lead to unfavorable operation conditions and presents a serious safety risk.